Integrated DC electroluminescent display system

ABSTRACT

An integrated electroluminescent display (DCEL), in which the DCEL (11) is integrted into the substrate board (10), such as, for example, a printed circuit board, which carries associated electronic components (12), such as, for example, those which would make up a control circuit, the DCEL displaying pertiment information for the control circuit. The bottom electrode (13) for the DCEL can be copper foil, which is etched at the same time as the rest of the foil pattern (13A) used to electrically interconnect the control components (12) of the overall control circuit during the making of the printed circuit board. Thereafter, the phosphor layer (14) is printed onto the associated copper foil segments, and, finally, a glass (15), which has on its inner surface an appropriate pattern of tin oxide (16), is placed on top of the phosphor depositions. The glass is then adhesively bonded to the printed circuit board and appropriate connections made between the tin oxide and the printed circuit board connectors with conductive adhesives, and a sealant (17) is applied around the edge of the glass to prevent moisture from entering the phosphor. Moisture traps (18) can be deposited before the glass is applied to surround each phosphor deposition. The P.C. board is thus made an integral, substrate part of the DCEL.

DESCRIPTION

1. Technical Field

The present invention relates to electroluminescent displays, and moreparticularly to variable electroluminescent displays which areelectrically or electronically controlled, and even more particularly tomethods of making such displays.

2. Background Art

Many control systems require changing displays to indicate status, setpoints, time, messages, and other information which is necessary forproper operation and process control.

Most of the displays that are currently used for this purpose are vacuumfluorescent displays which offer great economy. In addition to economy,as compared to other display techniques, the vacuum fluorescent displayhas gained wide market acceptance.

However, in spite of its economy, the display is either the mostexpensive or one of the most expensive components in a control system,with the display comprising for example, 15 to 25% of the total materialcost, often exceeding the cost of the microprocessor used in suchcontrol systems.

A display technology exists which can be used to achieve greatereconomies in the display technology, this display technology being knownas electroluminescent display (DCEL). This technology, generallyspeaking, has been around since approximately the mid-1940's. Itsprimary application until a few years ago has been predominantly as backillumination or panel illumination, used, for example, in airplanecockpits.

Within the last few years, advances in this technology, particularly inphosphor materials and drive techniques have made it possible to use theelectroluminescent approach for the display of intelligent information.Indeed, displays of high resolution, as well as simple segmented digitalformats, are used in automotive, telephone switching gear, computergraphic terminals, typewriter displays, etc.

Typically, in the prior art, the DCEL display is constructed as aseparate display component, with the component connected to appropriateelectronic circuits by a connector for operation. An exemplary prior artconstruction is illustrated in FIG. 1.

As shown in FIG. 1, the DCEL display of the prior art typically includesa glass substrate 1 (plain ordinary window glass will do), which iscoated with a transparent layer 2 of tin oxide. The tin oxide 2 isappropriately etched to form electrodes for the display.

On top of the tin oxide electrode 2, a layer 3 of phosphor is applied.On top of the phosphor 3, a second electrode 4 of, for example,aluminum, is formed either by screen printing, vapor deposition, orother techniques.

Moisture traps 6 are provided to absorb and hold any moisture which maybe present within the structure of the DCEL. A metal cover 6 completesthe assembly.

To make the display operational, it needs to be polarized. This is doneby applying a high voltage (e.g. 80-100 volts) for a period of timebetween the two electrodes. This causes migration of the phosphormolecules, so as to form a junction with the tin oxide/phosphorinterface 2/3. This migration also establishes the polarity of voltagerequired for display operations.

Although most of today's DCEL displays emit a yellow/orange light, otherphosphors can be used to provide other display colors. In addition tothe foregoing exemplary prior art structure, other variants have beensuggested.

Electroluminescent displays have been presented in various forms. Onepatentee has been Thomas L. Robinson, who has received U.S. Pat. Nos.3,786,307 (issued Jan. 15, 1974), 3,803,437 (issued April 9, 1974) and4,159,559 (issued July 3, 1979). For example, in the '307 patent theelectroluminescent display panel is mounted on a printed circuit boardas a separable element and in the preferred embodiment is secured to thecircuit board by means of screws having offset spaces between thedisplay panel and the printed circuit board. The display panel includesas part of its integrated structure its electrode strips. Thus, althoughthe panel is mounted on the printed circuit board, it is included as aseparate, separable element which is self-contained independently of theprinted circuit board. Indeed, one of the stated advantages of thedesign of the '307 patent, stated to be one of its "main advantages," isthat the electroluminescent portion can be a separate detachable part ofthe display assembly by making the bottom electrode part of anotherassembly. In the '307 patent the bottom electrode part includes aplurality of spaced, parallel metal strips or conductors secured on theupper face of the printed circuit board.

For further general background information reference is made to the pastDCEL products made by Phosphor Products Co., Ltd., for example its "2000Character DC Electroluminescent Display," a copy of its preliminaryspecification sheet dated June, 1984, being filed with this application.

DISCLOSURE OF THE INVENTION

In contrast to the prior art, the present invention integrates theelectroluminescent display into the overall electronic circuitry, forexample, the control circuitry, with the substrate for the display beinga board which supports or carries the electronic circuitry, for example,a printed circuit board, or alternatively ceramics, insulated metals, ormolded PC boards, etc.

Thus, the present invention constructs the DCEL display on, for example,the printed circuit board substrate, that is the same substrate to whichall the other control or other electrical components are placed and arecarried and supported.

This can be achieved, for example, by providing the segment pattern forthe DCEL display to be etched on the copper foil along with the rest ofthe foil pattern that is used for interconnecting the control or otherelectrical components. On top of the etched copper segment patterns isprinted the phosphor layer. Finally, a glass, which has on its innersurface a pattern of tin oxide is placed on top of the phosphordepositions, with the glass being adhesively bonded to the printedcircuit board with appropriate connections being made between the tinoxide and the printed circuit board connectors with conductiveadhesives. A RTV (room temperature vulcanizing) seal or some othersuitable material is applied around the edge of the glass to preventmoisture from entering the phosphor.

In essence, the construction of the present invention is the reverse ofwhat is typically done in constructing DCEL panels in the prior art.

Thus, the present invention includes a process which includes, forexample, depositing phosphor compound and other display components untoa printed wiring or circuit board or other like substrate that alsocontains and carries other electronic components, so that the displaybecomes an integral part of the electronic assembly substrate.

For example, the deposition of the phosphor is accomplished by printingof the phosphor in a desirable pattern unto conductor targets on theprinted wiring board. These conductors in turn connect with appropriatedrive components, which also are on the same printed wiring board.

Additionally, the present invention can include the deposition ofmoisture traps in such a fashion as to surround each phosphordeposition.

Likewise, the present invention includes having a layer of a transparentconductor deposited unto the glass, which in turn is adhesively bondedto the printed wiring board, with the conductively-coated surface of theglass being in direct contact with the deposited phosphor.

The conductive coating of the glass is then connected to additionalconductors on the printed wiring board, preferably with conductiveadhesives.

Finally, the edges of the display boundary are preferably further sealedagainst moisture and other contaminants.

The present invention thus provides a most cost effective constructionof, for example, control systems having an integrated DCEL display.

The foregoing and other features and advantages of the present inventionwill become more apparent from the following further description anddrawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side, simplified, cross-sectional view of an exemplary DCELdisplay constructed in accordance with typical prior art principles.

FIG. 2 is a side, cross-sectional view of an exemplary, preferredembodiment of the integrated DCEL display of the present invention, withthe display integrated into the exemplary printed circuit board carryingthe other associated control circuit electronic components.

FIG. 3 is a simplified, flow chart outlining the basic manufacturingsteps followed in the preferred methodology of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

As indicated above, in contrast to the prior art approach ofconstructing the DCEL as a separate component, such as that illustratedin FIG. 1 and with reference to FIG. 2, the present invention integratesthe electroluminescent display 11 into the overall electronic circuitry,for example, the control circuitry, with the substrate 10 for thedisplay also being the substrate or board which supports or carries theelectronic circuitry and components 12 for the control circuitry, suchas, for example, resistors, capacitors, transistors, etc, includingdrivers for the display 11, as part of the control circuitry, whichcause the DCEL to display intelligent images. An exemplary driver forthe display 11 would be a "Sprague" Part No. UCN 5810A. The othercomponents 12 can be pin mounted with soldered junctions 12A, as shown,or can be surface mounted, if so desired, or otherwise provided on thesubstrate board 10.

Thus, the present invention constructs the DCEL display 11 on, forexample, the printed circuit board substrate 10, that is on the samesubstrate to which all the other control or other electrical components12 are placed and are carried and supported.

This is achieved, for example, in the preferred, exemplary method of thepresent invention by providing the segment pattern 13 for the DCELdisplay 11 to be etched on the copper foil, along with the rest of thefoil pattern 13A that is used for electrically interconnecting thecontrol or other electrical components to form the printed controlcircuitry. As is known, the etched conductive layers 13 & 13A are verythin and by themselves would be insufficient in their inherentstructural strength to be used as a separate or separable element andindeed rely on the substrate 10 for the structural rigidity to holdtheir form. These layers 13A are typically formed by photographic"printing" techniques, using various screening, etching and platingprocesses, as is well known in the art.

On top of the etched copper segment patterns 13 is "printed" orotherwise suitable deposed the adjacent phosphor layers 14.

Finally, a glass element 15, typically rectangular in shape and whichhas on its inner surface a deposited pattern of tin oxide 16, is placedon top of the phosphor depositions 14, with the glass 15 beingadhesively bonded to the printed circuit board 10. The glass 15 formsthe viewing surface for the DCEL. The transparent, conductively-coated,tin oxide surface 16 of the glass 15 is in direct, electricallyconductive contact with the deposited phosphor layers 14, and theappropriate electrical connections are made between the tin oxide 16 andthe printed circuit board connectors, preferably with conductiveadhesives.

A RTV (room temperature vulcanizing) seal 17 or some other suitablematerial is applied around the edges 15A of the glass 15 to preventmoisture from entering the phosphor layers 14. Additionally, the presentinvention can include the deposition of moisture traps 18, in such afashion as to surround each phosphor deposition layer 14.

Thus, in essence, the construction of the present invention, assummarized in the flow diagram of FIG. 3, is the reverse of what istypically done in constructing DCEL panels in the prior art.

As noted above, the substrate preferably is, for example, a printedcircuit board 10. Alternatively, in place of the standard P.C. board asthe substrate, ceramics, insulated metals, or molded PC boards, etc.,could be used.

Although this invention has been shown and described with respect to adetailed, exemplary embodiment thereof, it should be understood by thoseskilled in the art that various changes in form, detail, methodologyand/or approach may be made without departing from the spirit and scopeof this invention.

Having thus described at least one exemplary embodiment of theinvention, that which is claimed as new and desired to be secured byLetters Patent is claimed below:
 1. An electroluminescent display (DCEL)system, including a printed circuit substrate, comprising:an electronicassembly substrate having printed circuit means thereon for electricallyinterconnecting other electrical components in addition to the DCEL;DCEL printed conductive segment patterns on said substrate having atleast the same general physical characteristics as said printed circuitmeans, having been made on said substrate concurrently with said printedcircuit means; DCEL phosphor layer(s) on top of the etched conductivesegment patterns; and a glass element having on its inner surface a DCELpattern of tin oxide positioned over the phosphor depositions, saidglass element being affixed to said substrate and said pattern of tinoxide being electrically interconnected into said printed circuit means;the DCEL being an integral part of the electronic assembly substrate,and the substrate being an integral part of the DCEL.
 2. Theelectroluminescent display (DCEL) system of claim 1, wherein there isfurther included:a moisture sealing material around the edge of saidglass element preventing exterior moisture from entering said phosphorlayer(s).
 3. The electroluminescent display (DCEL) system of claim 1,wherein there is further included:a series of moisture traps surroundingeach phosphor layer absorbing any moisture within the DCEL.
 4. Theelectroluminescent display (DCEL) system of claim 1, wherein there isfurther included:a number of electrical components mounted on andcarried by said substrate, said electrical components being electricallyinterconnected by said printed circuit means.
 5. The electroluminescentdisplay (DCEL) system of claim 1, wherein said electrical components,said printed circuit means and the DCEL form a control circuit.
 6. Anelectroluminescent display (DCEL) control circuit system, including aprinted circuit substrate, comprising:an electronic assembly substratehaving printed circuit means thereon for electrically interconnectingother electrical components in addition to the DCEL; DCEL printedconductive segment patterns on said substrate having at least the samegeneral physical characteristics as said printed circuit means, havingbeen made on said substrate concurrently with said printed circuitmeans; DCEL phosphor layer(s) on top of the etched conductive segmentpatterns; a glass element having on its inner surface a DCEL pattern oftin oxide positioned over the phosphor depositions, said glass elementbeing affixed to said substrate and said pattern of tin oxide beingelectrically interconnected into said printed circuit means; the DCELbeing an integral part of the electronic assembly substrate, and thesubstrate being an integral part of the DCEL; and a number of electricalcomponents mounted on and carried by said substrate, said electricalcomponents being electrically interconnected by said printed circuitmeans together and to the DCEL, forming a control circuit.
 7. Theelectroluminescent display (DCEL) system of claim 6, wherein there isfurther included:a moisture sealing material around the edge of saidglass element preventing exterior moisture from entering said phosphorlayer(s).
 8. The electroluminescent display (DCEL) system of claim 6,wherein there is further included:a series of moisture traps surroundingeach phosphor layer absorbing any moisture within the DCEL.
 9. Theelectroluminescent display (DCEL) system of claim 6, wherein saidelectrical components include:drive component means electricallyconnected to the DCEL for driving the DCEL, causing it to displayintelligent images.